Candidate Moderation under Instant Runoff and Condorcet Voting: Evidence from the Cooperative Election Survey

2026-03-03

AI Summary

This study investigates whether the purported advantage of Condorcet methods over Instant Runoff Voting (IRV) in promoting candidate moderation remains robust under realistic voter behavior. Leveraging data from the Cooperative Election Study (CES), the authors develop a more empirically grounded simulation framework that integrates a one-dimensional spatial model with incomplete and partial ballot rankings—conditions commonly observed in real-world elections. This approach enables the first comparative analysis of these ranked-choice voting systems under non-ideal, empirically plausible assumptions. The findings reveal that the moderating effect previously attributed to Condorcet methods diminishes significantly in realistic settings, substantially narrowing the gap with IRV. These results challenge theoretical claims that overstate the superiority of Condorcet methods and underscore the critical importance of incorporating actual voter behavior into institutional evaluations.

Technology Category

• Game Theory and Economic Paradigms: Social Choice / Voting
• Machine Learning: Learning Preferences or Rankings
• Knowledge Representation and Reasoning: Preferences

Application Category

• User Modeling, Personalization and Recommendation: Fairness-aware retrieval and ranking
• Search and Retrieval-Augmented AI: Web learning to rank, online learning, and counterfactual learning for ranking
• Web Mining and Content Analysis: Robustness and generalizability of Web mining methods

Abstract

This article extends the analysis of Atkinson, Foley, and Ganz in "Beyond the Spoiler Effect: Can Ranked-Choice Voting Solve the Problem of Political Polarization?". Their work uses a one-dimensional spatial model based on survey data from the Cooperative Election Survey (CES) to examine how instant-runoff voting (IRV) and Condorcet methods promote candidate moderation. Their model assumes an idealized electoral environment in which all voters possess complete information regarding candidates' ideological positions, all voters provide complete preference rankings, etc. Under these assumptions, their results indicate that Condorcet methods tend to yield winners who are substantially more moderate than those produced by IRV. We construct new models based on CES data which take into account more realistic voter behavior, such as the presence of partial ballots. Our general finding is that under more realistic models the differences between Condorcet methods and IRV largely disappear, implying that in real-world settings the moderating effect of Condorcet methods may not be nearly as strong as what is suggested by more theoretical models.

Problem

• candidate moderation
• instant-runoff voting
• Condorcet methods
• partial ballots
• voter behavior

Innovation

• ranked-choice voting
• Condorcet methods
• voter behavior modeling
• partial ballots
• candidate moderation